This invention relates to thermally bonded aluminosilica products and, more particularly, to thermally bonded aluminosilicate fibrous products of a novel and advantageous composition suited for use as diesel soot filters, kiln furniture, combustor liners, burner tubes and other high temperature applications.
Ceramic fibers are often used to provide thermal insulation from very high tempertures. For many applications, it is convenient and often necessary to form the fibers into rigid shapes such as boards or specialty configurations. Two approaches are used to accomplish bonding of ceramic fibers to obtain these shapes. Chemical bonding is the most common. A heat or air setting binder, usually in the liquid form, is added to the fiber and through drying, the application of low to moderate heat, or chemical reaction, the binder becomes rigid and literally glues the fibers into a rigid structure. Such binders include colloidal oxide suspensions, silicate solutions and thermoplastic suspensions. The strength of these systems are relatively low, typically having 20 to 50 psi flexural strength properties. More binder can be added to increase the strength. However, the additional binder adversely affects thermal insulating properties.
A second family of rigid ceramic shapes has been developed that utilizes more expensive firing schedules to sinter or fuse the fibers into a rigid structure. Flexural strengths are 10 to 20 times that of chemical bonding at the same density with no sacrifice in insulating properties. Difficulties in matching thermal expansion and preventing destructive crystal growth in the fibers have been experienced. Some success has been reportedly achieved through the use of a blend of silica fibers and aluminoborosilicate fibers. This technology still depends on the use of very expensive, high purity fibers and teaches against the use of lower grade fibers or lower grade particulates.